This invention relates to an improved wave guide for any mechanically scanned antenna and, more particularly, to a flexible wave guide joint which is more reliable than prior constructions.
The present construction is directed towards a motor vehicular collision warning system which includes a scanned beam sensor, a signal processor, and a vehicle interface system that initiates warnings to the driver or adaptively controls the vehicle. In this forward looking collision warning system, the sensor is designed to project a narrow beam of energy toward objects in the forward field of view. A forward collision warning control of this type for a vehicle can require a unit life in excess of two hundred million cycles at temperatures ranging from xe2x88x9240xc2x0 to 100xc2x0 C. Thus, reliability requirements are high and unit costs must be low.
Due to their weight and bulk, it is not practical to place a transceiver of a radar system on the moving mass of a rotated antenna in a motor vehicular collision warning system. Nevertheless, it is important that an efficient low loss microwave frequency connection be achieved in order to ensure adequate overall system performance. In certain prior constructions, a wave guide rotary joint has been used to achieve the coupling function.
Prior wave guide rotary joints are bulky and expensive. Some require full 360xc2x0 rotation. Further, while a rotary joint has reasonably good electrical performance at microwave frequencies, its performance at millimeter wave frequencies, especially higher than 40 GHz is not satisfactory, i.e., greater than 1 dB of insertion loss and variation of performance with rotation. A rotary joint is also expensive due to precision machined parts and bearings. Moreover, the reliability of rotary joints is marginal in systems requiring a very high number of rotations.
Therefore, it is an objective of the present invention to provide a flexible wave guide joint that has improved electrical performance, is less costly to produce, and is more reliable than prior constructions such as a rotary joint.
In accordance with this invention, a radar apparatus is provided with a low loss coupling between wave guides that is flexible in angular position. A rotatable slotted wave guide antenna is driven to oscillate back and forth at a small angle. A transceiver is coupled to a first wave guide portion that is held in a fixed position with an open end facing a second wave guide portion also having an open end. A small air gap exists between the open ends of the two wave guide portions wherein the air gap varies with angular rotation of the non-fixed wave guide portion.
The initial position for the moveable wave guide portion is with its longitudinal axis coincident with the fixed wave guide longitudinal axis. The air gap between the two wave guide portions is small thereby providing for low insertion loss. As the moveable wave guide angularly rotates, the gap between the open end walls of the two wave guide portions varies. The maximum angular rotation between the wave guide portions is limited by the gap between the open end walls. For a maximum angle, the wave guide portions should be positioned so that the air gap varies between the walls that are closest together. Thus, the present invention provides a wave guide coupling which allows angular motion between two wave guide portions with minimal effort and without bending or sliding parts that would result in performance degradation in use.
A small air gap is needed to keep the insertion loss of the joint to a minimum. The minimum air gap is determined by preventing the walls of the wave guide portions from butting into each other at a maximum angular rotation. With the present construction, there is no need for dielectric or other spacers in the air gap region. Further, no chokes or mode suppressors are required to obtain the low insertion loss.
Thus, in one embodiment of the invention, a wave guide antenna is provided which includes a center feed with a plurality of slotted apertures to pass transmitted and reflected radar signals to and from the target. A two-part wave guide feed is also provided with one part of the wave guide feed being coupled to the transceiver. This wave guide portion is also fixed relative to the other wave guide feed portion. The other portion of the wave guide feed is integral with the antenna and is separated from the first portion by the previously described air gap. When the antenna is oscillated, the moveable wave guide feed portion rotates angularly relative to the fixed wave guide feed portion.
The foregoing and other advantages and features of the invention will be more apparent from the following description when taken in connection with the accompanying drawings.